I don't buy that. Again, it's a biological phase like puberty. A baby will eat nearly anthying their parents give them. Upon reaching a certain age, they'll begin to reject some foods. That has several different possible reasons.
For instance, your example of having to "stay strong in the face of adversity" may cause the exact opposite of what you want.
Ever watched a small child fall down and, say, bump its knees? Sometimes it will look around and see if anyone noticed. If the mother watched, then it will begin to cry, the mother will make a fuss over it and so on. Happens because the kid knows that if it cries, it will get attention.
Same thing with food. Sometimes it's not so much about the food itself, it's about the attention. Any kind of attention. And if they get that attention, it will reinforce that particular behaviour.
Sometimes it's best to simply ignore it.
When the stars threw down their spears
And watered heaven with their tears:
Did he smile his work to see?
Did he who made the lamb make thee?
The proccess of "wanting attention" is not limited to babies. It also works for toddlers, schoolchildren, teenagers and adults. It's basic psychology - and it does not simply disappear with age. If anything, it becomes more sophisticated.
I myself can remember at least two occasions in my adult life where I did something pretty daft to get attention from someone who I thought was neglecting me.
Or did you never hear of the tactic: "I want his/her attention, so I'll flirt with someone else and make him/her jealous"? Same thing, really.
When the stars threw down their spears
And watered heaven with their tears:
Did he smile his work to see?
Did he who made the lamb make thee?